Fuel cell

ABSTRACT

In this fuel cell, a cathode-side porous film that covers a cathode electrode is interposed between the cathode electrode and an air supply layer, the cathode electrode constituting electrolyte film/electrode structures. In addition, breathing holes are formed in the cathode-side porous film, and the air flowing through air supply passages passes through the breathing holes and is supplied to the cathode electrode.

TECHNICAL FIELD

The present invention relates to a fuel cell including a membraneelectrode assembly formed by providing a plurality of anodes and aplurality of cathodes for one electrolyte membrane.

BACKGROUND ART

A typical fuel cell is formed by stacking a plurality of unit cellstogether. Each of the unit cells is obtained by sandwiching a membraneelectrode assembly (MEA) between a pair of separators. This structure isknown as a fuel cell stack. In contrast, in recent years, it is proposedto provide a plurality of anodes and a plurality of cathodes for oneelectrolyte electrode assembly to form a plurality of unit cells havinga planar shape.

As described in Japanese Laid-Open Patent Publication No. 2011-204609,in this case, interconnecting sections are formed in the electrolytemembrane for electrically connecting the adjacent unit cells together.That is, a plurality of unit cells are connected in series through theinterconnecting sections. In the case of adopting the structure, a highvoltage fuel cell can be obtained using one electrolyte membrane, and nooperation of stacking the unit cells together is requiredadvantageously.

SUMMARY OF INVENTION

In a typical fuel cell, as a coolant, coolant liquid such as coolantwater is supplied into the stack. However, in this case, since amechanism for supplying/discharging the coolant liquid is required, thesize of the fuel cell may become large, and the structure of the fuelcell may be complicated. In an attempt to address the problem, in thefuel cell of the above type, it may be considered to use the air as theoxygen-containing gas, and use the air as the coolant.

However, in this case, the cathode is exposed to the air flowing insidethe fuel cell. Therefore, there is a concern that the cathode and/or theelectrolyte membrane are dried excessively. Under the circumstances,since the proton conductivity of the electrolyte membrane is decreased,the power generation characteristic of the fuel cell is decreased.

A main object of the present invention is to provide a fuel cell inwhich the air flowing inside the fuel cell is supplied to a cathode.

Another object of the present invention is to provide a fuel cell whichmay eliminate the concern of excessive drying of the cathode.

According to an aspect of the present invention, a fuel cell including amembrane electrode assembly is provided. The membrane electrode assemblyincludes a single electrolyte membrane in which interconnecting sectionsare formed, the interconnecting sections extending in a first directionand having conductivity in a membrane thickness direction of theelectrolyte membrane, a plurality of anodes extending in the firstdirection, and disposed remotely from each other in a second directionperpendicular to the first direction, and a plurality of cathodesextending in the first direction, and disposed remotely from each otherin the second direction, wherein the membrane electrode assembly has azigzag layout where, in the second direction, part of one of the anodesfaces part of one of two cathodes that are adjacent to each other, amongthe cathodes, through the electrolyte membrane and another part of theone anode faces part of the remaining one of the two cathodes throughone of the interconnecting sections formed in the electrolyte membrane,the fuel cell further includes a cathode side porous film configured tocover the plurality of cathodes, the cathode side porous film havingbreathing holes for supplying an oxygen-containing gas to the pluralityof cathodes, and an oxygen-containing gas supply layer provided adjacentto the cathode side porous film, and an oxygen-containing gas supplychannel as a passage of the oxygen-containing gas being formed in theoxygen-containing gas supply layer.

That is, in the present invention, a cathode side porous film isinterposed between the oxygen-containing gas supply layer and thecathodes. This cathode side porous film holds water produced at thecathodes. It is because the produced water is not discharged to theoutside of the cathode side porous film without being discharged throughthe breathing holes.

Therefore, the cathodes and/or the electrolyte membrane which contactsthe cathodes are humidified suitably. Stated otherwise, it is possibleto avoid excessive drying of the cathodes and/or the electrolytemembrane. As a result, the electrolyte membrane exhibits suitable protonconductivity. Therefore, the fuel cell has suitable power generationcharacteristics.

Additionally, by adopting the above structure, it is possible to use theoxygen-containing gas (e.g., the air) as the coolant for cooling thefuel cell. Also in this case, as described above, because it is possibleto avoid excessive drying of the cathodes and/or the electrolytemembrane by the cathode side porous film. Accordingly, it is possible toreduce the size of the fuel cell, and simplify the structure of the fuelcell.

For example, the oxygen-containing gas supply channel can be formed in amanner to extend in the first direction. In this case, it is possible tomake the oxygen-containing gas contact the cathodes entirely in alongitudinal direction (first direction).

Further, it is adequate that the fuel cell may further include anegative pressure generation unit configured to cause theoxygen-containing gas supply channel to have a negative pressure. Theoxygen-containing gas can be guided from the outside of the fuel cellinto the oxygen-containing gas supply channel having the negativepressure. That is, it becomes possible to allow the oxygen-containinggas to flow inside the fuel cell easily.

In the present invention, the water produced at the cathodes is held bythe cathode side porous film interposed between the oxygen-containinggas supply layer and the cathodes. Thus, excessing drying of thecathodes and/or the electrolyte membrane which contacts the cathodes isavoided, and the cathodes and/or the electrolyte membrane are suitablykept humidified. Therefore, the fuel cell has suitable power generationcharacteristics.

Further, since the oxygen-containing gas (e.g., air) can be used as thecoolant for cooling the fuel cell, it is possible to reduce the size ofthe fuel cell, and simplify the structure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an overall perspective view schematically showing a fuel cellaccording to an embodiment of the present invention;

FIG. 2 is an exploded perspective view showing main components of thefuel cell in FIG. 1 ;

FIG. 3 is a vertical cross sectional view showing main components of afuel cell in FIG. 1 ;

FIG. 4 is a schematic plan view showing an An side film (anode sideporous film) of a laminate layer;

FIG. 5 is an overall perspective view showing an air supply layer(oxygen-containing gas supply layer) of the fuel cell;

FIG. 6 is an overall schematic perspective view showing a lower sidehydrogen supply layer (fuel gas supply layer) of the fuel cell; and

FIG. 7 is a schematic plan view showing flow directions of hydrogen whena plurality of fuel cells are coupled together in parallel.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a preferred embodiment of the present invention will bedescribed with reference to the accompanying drawings. The followingexpressions “lower”, “upper”, “left”, and “right” correspondparticularly to the lower side, the upper side, the left side, and theright side in FIG. 3 . However, these directions are defined for ease ofunderstanding the present invention, and are not intended to define thedirections when the fuel cell is used.

FIG. 1 is an overall perspective view schematically showing a fuel cell10 according to the embodiment, FIG. 2 is an exploded perspective viewshowing main components of the fuel cell 10 according to the embodiment,and FIG. 3 is a vertical cross sectional view showing main components ofthe fuel cell 10 according to the embodiment. In the fuel cell 10, alower housing member 12, a support panel 14 of an oxygen-containing gassupply layer 70 described later, an upper housing member 16, and a fanattachment member 18 shown in FIG. 1 are assembled together to form asubstantially rectangular parallelepiped housing 20.

As shown in FIGS. 2 and 3 , a first structural body 22 a as a firstmembrane electrode assembly on the lower side and a second structuralbody 22 b as a second membrane electrode assembly on the upper side areaccommodated in the housing 20. Firstly, the first structural body 22 aand the second structural body 22 b will be described. It should benoted that the structural bodies 22 a, 22 b have substantially the samestructure. However, for ease of explanation, in FIGS. 2 and 3 , thefirst structural body 22 a positioned on the lower side will be referredto as the “lower MEA”, and the second structural body 22 b positioned onthe upper side will be referred to as the “upper MEA”. Further, in thefollowing description, the “Ca side” and the “An side” mean the sidecloser the cathode, and the side closer to the anode, respectively.

As shown in FIG. 3 in detail, the lower MEA 22 a includes a singleelectrolyte membrane 24. A plurality of anodes 26 are formed on thelower end surface of the electrolyte membrane 24, and a plurality ofcathodes 28 are formed on an upper end surface of the electrolytemembrane 24. Specifically, on the lower end surface of the electrolytemembrane 24, an An side protection layer 30, an An side electrodecatalyst layer 32, and an An side gas diffusion layer 34 are stackedtogether in this order from the side closer to the electrolyte membrane24 to form one anode 26. The An side protection layer 30, the An sideelectrode catalyst layer 32, and the An side gas diffusion layer 34 forma band shape extending in a direction indicated by an arrow A (firstdirection) in FIG. 1 . That is, the anode 26 extends in the longitudinaldirection indicated by the arrow A.

The width of the An side electrode catalyst layer 32 in the directionindicated by the arrow B (second direction) is smaller than the width ofthe An side protection layer 30 and the width of the An side gasdiffusion layer 34. Therefore, the An side protection layer 30 and theAn side gas diffusion layer 34 are partially in direct contact with eachother. It should be noted that the An side protection layer 30 is a thinmembrane of perfluorosulfonic acid containing water.

A plurality of the anodes 26 having the above structure are arranged inthe direction indicated by the arrow B. The adjacent anodes 26 arespaced from each other through an An side groove 36.

On the other hand, on the upper end surface of the electrolyte membrane24, a Ca side protection layer 38, a Ca side electrode catalyst layer40, and a Ca side gas diffusion layer 42 are stacked together in thisorder from the side closer to the electrolyte membrane 24 to form onecathode 28. The Ca side protection layer 38, the Ca side electrodecatalyst layer 40, and the Ca side gas diffusion layer 42 form a bandshape extending in the direction indicated by the arrow A (firstdirection) shown in FIGS. 1 and 2 . That is, as in the case of the anode26, the cathode 28 extends in the longitudinal direction indicated bythe arrow A.

It should be noted that the width of the Ca side electrode catalystlayer 40 and width of the Ca side gas diffusion layer 42 in thedirection indicated by the arrow B (second direction) are substantiallythe same. In contrast, the Ca side protection layer 38 is formed in amanner that a plurality of non-contact holes 46 are scattered along thedirection (direction indicated by the arrow A) in which interconnectingsections 44 described later extends. Further, for example, the Ca sideprotection layer 38 is made of thin membrane of perfluorosulfonic acidpolymer containing carbon black.

The plurality of the cathodes 28 having the above structure are providedin the direction indicated by the arrow B. The cathodes 28 that areadjacent to each other are spaced from each other through a Ca sidegroove 48.

The Ca side grooves 48 are formed at positions offset from the An sidegrooves 36. Further, the interconnecting section 44 is positionedbetween the An side groove 36 and the Ca side groove 48. Therefore, theone anode 26 is bridged over the two cathodes 28 that are adjacent toeach other through the Ca side groove 48. That is, a zigzag layout isadopted in a manner that, in the direction indicated by the arrow B,part of one anode 26 faces part of one of the cathodes 28 through theelectrolyte membrane 24, and another part of the anode 26 faces part ofanother one of the adjacent cathodes 28 through one of theinterconnecting sections 44. The part of the anode 26 and the part ofthe cathode 28 that face each other through the electrolyte membrane 24form a unit cell 50.

The interconnecting sections 44 formed in the electrolyte membrane 24are provided over the electrolyte membrane 24 in the membrane thicknessdirection from the An side protection layer 30 to the Ca side protectionlayer 38, and have a band shape extending in the direction indicated bythe arrow A. In the electrolyte membrane 24, electron conduction occursmainly in the interconnecting sections 44, and proton conduction occursmainly in portions other than the interconnecting sections 44.

The lower MEA 22 a having the above structure is laminated by an An sidefilm 52 (anode side porous film) and a Ca side film 54 (cathode sideporous film). That is, the An side film 52 and the Ca side film 54 havethe large area in comparison with the lower MEA 22 a, and the outermarginal portions of the An side film 52 and the Ca side film 54 exposedfrom the lower MEA 22 a are joined together. Thus, a laminate layer 56is formed.

The An side film 52 and the Ca side film 54 are made of material havingheat resistance in the operating temperature (several tens to 100° C.)of the fuel cell 10 such as resin. In particular, it is preferable ifthe An side film 52 and the Ca side film 54 are made of transparentresin, because it is possible to visually and easily recognize the statewhere, e.g., the lower MEA 22 a is enclosed, and the An side film 52 andthe Ca side film 54 are joined together. Specific examples of such resininclude polyimide resin.

The lower MEA 22 a is thin. Though the lower MEA 22 a is softsufficiently to be warped by its own weight when only the lower MEA 22 ais held, rigidity of the lower MEA 22 a is increased to some extent byenclosing the lower MEA 22 a into the laminate layer 56. That is, to theextent that the lower MEA 22 a and the laminate layer 56 are heldaltogether, the lower MEA 22 a is not warped by its own weight.Therefore, it becomes easy to handle the lower MEA 22 a, e.g., transportthe lower MEA 22 a. Further, since the shape of the lower MEA 22 a ismaintained, it is possible to avoid deformation such as warpage of thelower MEA 22 a.

As shown in FIG. 4 , the An side film 52 is provided in tight contactwith the plurality of the anodes 26, respectively. The An side film 52includes a plurality of first straight segments 60 superimposed on theinterconnecting sections 44, and extend in the direction indicated bythe arrow A, and a plurality of second straight segments 62 extending inthe direction indicated by the arrow B perpendicular to the firststraight segments 60. That is, the An side film 52 has a lattice shapewhere the first straight segments 60 and the second straight segments 62extend perpendicularly to each other. By intersection of the two firststraight segments 60 and the two second straight segments 62, an An sidebreathing hole 64 having a substantially rectangular shape surrounded bythe four straight segments 60, 60, 62, 62 is formed.

On the other hand, Ca side breathing holes 66 are formed in the Ca sidefilm 54 (see FIG. 3 ). The thickness of the Ca side film 54 is smallerthan the thickness of the An side film 52. Stated otherwise, thethickness of the An side film 52 is larger than the thickness of the Caside film 54.

The upper MEA 22 b has substantially the same structure as the lower MEA22 a. Therefore, the constituent elements of the upper MEA 22 b that areidentical to those of the lower MEA 22 a are labelled with the samereference numerals, and the description thereof is omitted.

In the lower MEA 22 a, the anode 26 is provided below the electrolytemembrane 24, and the cathode 28 is provided above the electrolytemembrane 24. In the upper MEA 22 b, the cathode 28 is provided below theelectrolyte membrane 24, and the anode 26 is provided above theelectrolyte membrane 24. That is, in the fuel cell 10, the cathode 28 ofthe lower MEA 22 a and the cathode 28 of the upper MEA 22 b face eachother.

The unit cells 50 of the lower MEA 22 a and the unit cells 50 of theupper MEA 22 b are in different phases. That is, positions of the Anside grooves 36, the Ca side grooves 48, and the interconnectingsections 44 of the lower MEA 22 a are determined to be positions offsetfrom the An side grooves 36, the Ca side grooves 48, and theinterconnecting sections 44 of the upper MEA 22 b.

An air supply layer 70 (oxygen-containing gas supply layer) shown indetail in FIG. 5 is inserted between the lower MEA 22 a and the upperMEA 22 b. For example, the air supply layer 70 is made of materialhaving high heat conductivity such as aluminum, copper, or alloy of thealuminum and copper, and includes a fin 76 having a wavy shape wherelower protrusions 72 (first protrusions) and upper protrusions 74(second protrusions) are arranged alternately. The lower protrusions 72contact the Ca side film 54 of the lower MEA 22 a, and the upperprotrusions 74 contact the Ca side film 54 of the upper MEA 22 b. Itshould be noted that insulating treatment may be applied to the surfaceof the fin 76.

The lower protrusions 72 are superimposed on the interconnectingsections 44 of the electrolyte membrane 24 of the lower MEA 22 a (seeFIG. 3 ). Further, the upper protrusions 74 are superimposed on theinterconnecting sections 44 of the electrolyte membrane 24 of the upperMEA 22 b. That is, the fin 76 has a wavy shape where the lowerprotrusions 72 correspond to the positions of the interconnectingsections 44 of the lower MEA 22 a, and the upper protrusions 74correspond to the positions of the interconnecting sections 44 of theupper MEA 22 b.

A space extending in the direction indicated by the arrow A is formedbetween the lower protrusion 72 and the Ca side film 54 of the upper MEA22 b. Likewise, a space extending in the direction indicated by thearrow A is formed between the upper protrusion 74 and the Ca side film54 of the lower MEA 22 a as well. These spaces serve as upper air supplychannels 78 a (oxygen-containing gas supply channel) for suppling air(oxygen-containing gas) to the cathodes 28 of the upper MEA 22 b, andlower air supply channels 78 b (oxygen-containing gas supply channel)for supplying air to the cathodes 28 of the lower MEA 22 a.

The Ca side breathing holes 66 formed in the Ca side film 54 areconnected to the upper air supply channels 78 a or the lower air supplychannels 78 b. That is, the Ca side breathing holes 66 are formed atpositions which do not contact the lower protrusions 72 or the upperprotrusions 74.

Further, the air supply layer 70 includes the support panel 14 whichsupports the fin 76, and which is inserted between the upper housingmember 16 and the lower housing member 12 (see FIG. 5 ). The supportpanel 14 is provided with discharge ducts 80 which are opened atpositions adjacent to the fan attachment member 18 (on the front side)when the housing 20 is set-up, and inlet ducts 82 which are opened onthe rear side. As described above, the inlet ducts 82 are configured totake air flowing through the upper air supply channels 78 a and thelower air supply channels 78 b from the outside to the inside of thehousing 20. The discharge ducts 80 are configured to discharge the airflowing through the upper air supply channels 78 a and the lower airsupply channels 78 b to the outside of the housing 20.

The front ends of the inlet ducts 82 and the discharge ducts 80 areconfigured to be provided at positions slightly shifted from the frontend and the rear end of the support panel 14 toward the deeper sides.Therefore, a first buffer space and a second buffer space each havingpredetermined volume are formed between the inlet ducts 82 or thedischarge ducts 80 and the fan attachment member 18.

The support panel 14 is provided with two Ca side current collectors anda Ca side terminal (not shown) electrically connected to the cathodes 28of the lower MEA 22 a and the upper MEA 22 b individually, and two Anside current collectors and an An side terminal (not shown) electricallyconnected to the anodes 26 individually. The external load can beconnected electrically to the Ca side terminals and the An sideterminals.

Further, a lower side hydrogen supply layer 84 (fuel gas supply layer)for supplying the hydrogen gas as the fuel gas is provided below thelower MEA 22 a. An upper side hydrogen supply layer 86 (fuel gas supplylayer) in the form of a substantially flat plate is provided above theupper MEA 22 b as well. The lower side hydrogen supply layer 84 and theupper side hydrogen supply layer 86 are supported by the lower housingmember 12 and the upper housing member 16, respectively (see FIG. 2 ).

As shown in FIG. 6 , lower side hydrogen supply channels 88 (fuel gassupply channels) are formed on the end surface of the lower sidehydrogen supply layer 84 facing the anode 26 of the lower MEA 22 a, in amanner to be depressed downward from the end surface. The lower sidehydrogen supply channels 88 include a plurality of onward channels 90and return channels 92 extending in the direction indicated by the arrowB. The onward channels 90 and the return channels 92 are arrangedalternately in parallel to each other. Further, the onward channels 90and the return channels 92 are connected through connection channels 94extending in the direction indicated by the arrow A. That is, each ofthe lower side hydrogen supply channels 88 is a serpentine type channelhaving a so-called serpentine shape where the straight channels turnback through the connection channels 94.

In the lower side hydrogen supply layer 84, the lower side hydrogensupply channels 88 are grooves, and the other portions are walls. Asshown in FIG. 3 , the walls are bridged from the portion of one of theanodes 26 where the An side electrode catalyst layer 32 is not presentto the portion of another anode 26 adjacent to the one anode 26 wherethe An side electrode catalyst layer 32 is not present. Therefore, theAn side grooves 36 are closed by the walls. Further, the interconnectingsections 44 are superimposed on the walls through the anodes 26.

On the other hand, upper side hydrogen supply channels 96 (fuel gassupply channel) are formed on an end surface of the upper side hydrogensupply layer 86 adjacent to the anode 26 of the upper MEA 22 b, in amanner to be depressed upward from the end surface. Each of the upperside hydrogen supply channels 96 is a serpentine type channel includingthe onward channels 90, the return channels 92, and the connectionchannels 94, formed in the same manner as the lower side hydrogen supplychannels 88. Further, in the upper side hydrogen supply layer 86, thewalls other than the upper side hydrogen supply channels 96 in the formof a groove close the An side grooves 36, and are superimposed on theinterconnecting sections 44 through the anodes 26.

The lower housing member 12 and the upper housing member 16 are providedwith a lower supply manifold 100 and an upper supply manifold 102 forsupplying the hydrogen into the housing 20, and a lower dischargemanifold 104 and an upper discharge manifold 106 for discharging thehydrogen from the inside of the housing 20 (see FIG. 1 ). Further, thefan attachment member 18 attached in a manner to bridge over the lowerhousing member 12 and the upper housing member 16 is provided with a fan108 (negative pressure generation unit) for generating the negativepressure in the housing 20.

For example, the lower housing member 12 and the upper housing member 16are tightened together by fastening members such as bolts/nuts. By thistightening, the support panel 14 is held between the lower housingmember 12 and the upper housing member 16. Further, for example, the fanattachment member 18 is coupled to the lower housing member 12 and theupper housing member 16 by fastening members such as bolts/nuts.

The fuel cell 10 according to the embodiment of the present inventionbasically has the above structure. Next, operation and advantages of thefuel cell 10 will be described in relation to operation of the fuel cell10.

As described above, the lower MEA 22 a and the upper MEA 22 b areenclosed into the laminate layer 56 where the Ca side film 54 coveringall of the cathodes 28 and the electrolyte membrane 24 and the An sidefilm 52 covering all of the anodes 26 and the electrolyte membrane 24are joined together. Since the laminate layer 56 is hard enough not tobe warped by its own weight, the laminate layer 56 can be handledeasily. Therefore, at the time of assembling the fuel cell 10, forexample, it is possible to easily perform operation of inserting thelower MEA 22 a and the upper MEA 22 b between the lower housing member12 and the support panel 14 or between the support panel 14 and theupper housing member 16.

Further, as a result of tightening the lower housing member 12 and theupper housing member 16, the interconnecting sections 44 of theelectrolyte membrane 24 of the lower MEA 22 a are pressed by the lowerprotrusions 72 of the air supply layer 70 and the lower housing member12. Likewise, the interconnecting sections 44 of the electrolytemembrane 24 of the upper MEA 22 b are pressed by the upper protrusions74 of the air supply layer 70 and the upper housing member 16.Preferably, the pressing force against the lower MEA 22 a and the upperMEA 22 b is not more than 5 MPa.

Further, since a plurality of unit cells 50 are provided on the sameplane surface, it is possible to obtain the fuel cell 10 having a largeelectromotive force even though the fuel cell 10 has a small size.

At the time of operating the fuel cell 10, the external load (e.g.,motor, etc.) is electrically connected to the Ca side terminal, and theAn side terminal exposed to the outside of the housing 20. Further,while the temperature of the fuel cell 10 is increased to about severaltens to 100° C., rotation of the fan 108 is actuated, and hydrogen issupplied from a hydrogen supply source (not shown) into the housing 20through the lower supply manifold 100 and the upper supply manifold 102.

As a result of rotation of the fan 108, the air in the housing 20 (inparticular, the lower air supply channels 78 b and the upper air supplychannels 78 a) is sucked toward the fan 108. After the sucked air flowsfrom the discharge ducts 80 provided in the support panel 14 to thefirst buffer space, the air is discharged to the outside of the housing20 through the fan 108. Therefore, the pressure in the housing 20becomes a negative pressure.

The inlet ducts 82 provided in the support panel 14 are positioned onthe rear side of the housing 20. Since the pressure in the housing 20 isa negative pressure, the air outside the housing 20 is guided into thehousing 20 through the inlet ducts 82. The guided air is sucked by thefan 108. As a result, the air flows along the lower air supply channels78 b and the upper air supply channels 78 a toward the fan 108. That is,the air flows through the lower air supply channels 78 b and the upperair supply channels 78 a.

In this process, some of the air flows into the laminate layer 56through the Ca side breathing holes 66 formed in the Ca side film 54,and then, after the air is diffused through the Ca side gas diffusionlayer 42, the air reaches the Ca side electrode catalyst layer 40. Inthis manner, the air is supplied to the cathodes 28.

In the meanwhile, the hydrogen guided from the lower supply manifold 100into the housing 20 flows into the onward channels 90 of the lower sidehydrogen supply channels 88, and flows in the direction indicated by thearrow B. Further, hydrogen flows from the distal end of the onwardchannels 90 through the connection channels 94 and enters the returnchannels 92 to turn back, and then, flows again in the directionindicated by the arrow B. Also at the distal ends of the return channels92, the hydrogen flows through the connection channels 94, and entersthe onward channels 90 to turn back, and flows again in the directionindicated by the arrow B. That is, after the hydrogen flows from theanode 26 which is closest to the lower supply manifold 100 on theupstream side to move across each of the anodes 26, the hydrogen flowsback from the anode 26 which is closest to the lower discharge manifold104, and flows in a manner to move across each of the anodes 26 again.While repeating movement in such a serpentine pattern, the hydrogenmoves toward the lower discharge manifold 104.

In this process, some of the hydrogen enters the laminate layer 56through the An side breathing holes 64 formed in the An side film 52,and then, after the hydrogen is diffused through the An side gasdiffusion layer 34, the hydrogen reaches the An side electrode catalystlayers 32. That is, hydrogen is supplied to each of the anodes 26. Theredundant hydrogen is discharged to the outside of the housing 20 fromthe lower discharge manifold 104.

In each of the An side electrode catalyst layers 32, hydrogen is ionizedto produce protons and electrons. The protons are mainly conductedthrough the portion of the electrolyte membrane 24 other than theinterconnecting sections 44, and reach the Ca side electrode catalystlayers 40. In the meanwhile, the electrons move toward the cathode 28 ofthe adjacent unit cell 50 mainly through the interconnecting sections 44of the electrolyte membrane 24.

Further, at the cathode 28, in the Ca side electrode catalyst layer 40,the protons and the electrons, and the oxygen in the air are combinedtogether to produce water. The water moves together with, e.g.,hydrogen, and flows along the lower side hydrogen supply channels 88.Therefore, the hydrogen flowing through the lower side hydrogen supplychannels 88 becomes highly humidified as it moves toward the downstreamside (lower discharge manifold 104).

In the case where the onward channels 90 and the return channels 92 ofthe lower side hydrogen supply channels 88 extend in the directionindicated by the arrow A, after the hydrogen flows through the one anode26 to contact one of the anodes 26 entirely, the hydrogen flows in amanner to contact another anode 26 adjacent to the one anode 26entirely. That is, low humidity hydrogen contacts the anode 26 on theupstream side, and high humidity hydrogen contacts the anode 26 on thelower side. As described above, in the case where the hydrogen having adifferent humidity is supplied to each of the anodes 26, there is aconcern that the power generation amount of the unit cells 50 may vary,and power generation of the fuel cell 10 becomes unstable.

In contrast, in the present embodiment, the onward channels 90 and thereturn channels 92 of the lower side hydrogen supply channels 88 extendacross the plurality of the anodes 26. Therefore, the hydrogen contactsthe one anode 26 a plurality of times while increasing the humidity.That is, the hydrogen having a different humidity does not contact eachof the anodes 26. Therefore, the power generation amount of arbitraryone of the unit cells 50 and the power generation amount of the unitcell 50 which is different from this arbitrary unit cell 50 becomesubstantially the same. Thus, it is possible to eliminate the concernthat power generation of the fuel cell 10 becomes unstable.

Further, the interconnecting sections 44 are superimposed on the wallsof the lower side hydrogen supply layer 84 through the anodes 26, andthe walls of the upper side hydrogen supply layer 86 are superimposed onthe interconnecting sections 44 through the anodes 26. Therefore, thatis, the walls of the lower side hydrogen supply layer 84 and the upperside hydrogen supply layer 86 press the electrolyte membrane 24. As aresult, the shapes of the lower MEA 22 a and the upper MEA 22 b aremaintained.

The majority of the produced water is maintained within the laminatelayer 56. Therefore, since the lower MEA 22 a (in particular, theelectrolyte membrane 24) is maintained in the humidified state, thesufficient proton conductivity is obtained in the electrolyte membrane24. Further, since the laminate layer 56 is made of insulating material,it is possible to prevent short circuiting by the contact of the cathode28 and the fin 76.

The redundant produced water is discharged from the Ca side breathingholes 66 formed in the Ca side film 54 to the lower air supply channels78 b. In this regard, the Ca side breathing holes 66 are not formed inthe portions which contact the lower protrusions 72. Therefore, it ispossible to avoid electric conduction through liquid between the fin 76and the lower protrusions 72.

Further, the walls of the lower side hydrogen supply layer 84 and thefin 76 press the lower MEA 22 a. Therefore, the shape of the lower MEA22 a is maintained. Further, the interconnecting sections 44 are pressedby the lower protrusions 72 and the upper protrusions 74 of the fin 76,and the pressing force is efficiently transmitted to the interconnectingsections 44 through the first straight segments 60 of the An side film52. As a result, since the contact resistance at the contact interfacebetween the interconnecting sections 44 and the Ca side electrodecatalyst layers 40 is reduced, electronic conductivity becomes suitable.

Further, non-contact holes 46 scattered along the direction indicated bythe arrow A are formed at the positions of the Ca side protection layer38 corresponding to the positions of the interconnecting sections 44.Further, in each of the anodes 26, the An side electrode catalyst layer32 is not present at positions corresponding to the interconnectingsections 44 and the non-contact holes 46. Therefore, at the positionsadjacent to the non-contact holes 46, occurrence of the electrodereactions at the interface between the interconnecting sections 44 andthe Ca side electrode catalyst layer 40 or the An side electrodecatalyst layer 32 is suppressed. Stated otherwise, production of thewater is suppressed. Therefore, it is possible to avoid electricconduction through liquid resulting from the water produced excessivelyat the contact interface of the interconnecting sections 44, the cathode28, and the anode 26.

It is a matter of course that the above points are applicable to theupper MEA 22 b as well.

As described above, the operating temperature of the fuel cell 10 isabout several tens to 100° C. Further, as a result of inducing theelectrode reactions, the lower MEA 22 a and the upper MEA 22 b areheated. In this regard, the air flows through the lower air supplychannels 78 b and the upper air supply channels 78 a, and the fuel cell10 is cooled by this air. As a result, it is possible to avoid excessiveincrease in the temperature of the fuel cell 10. Thus, the fuel cell 10is a so-called air cooled fuel cell.

Further, since the lower MEA 22 a and the upper MEA 22 b are cooled bythe air (heat is removed), it is possible to avoid excessive drying ofthe cathodes 28. Further, the water produced in the electrode reactionsis prevented from being discharged to the outside from the positionsother than the Ca side breathing holes 66 and/or the An side breathingholes 64 formed in the laminate layer 56. That is, some volume of wateris stored in the laminate layer 56. By the above process, the humidityof the An side gas diffusion layer 34 and the humidity of the Ca sidegas diffusion layer 42 are maintained suitably. Therefore, since thehumidity of the electrolyte membrane 24 is maintained, the predeterminedproton conductivity is maintained.

The present invention is not limited to the above described embodiment.It is a matter of course that various modifications may be made withoutdeparting from the gist of the present invention.

For example, another MEA may be stacked on at least one of the positionbelow the lower MEA 22 a and the position above the upper MEA 22 b. Inthis case, it is adequate that the anode 26 forming the other MEA isoriented to face the anode 26 of the lower MEA 22 a or the anode 26 ofthe upper MEA 22 b.

Further, as shown in FIG. 7 , a plurality of the fuel cells 10 may bearranged in parallel in the horizontal direction. In this case, it isadequate that the hydrogen is guided in a manner that the hydrogen isdistributed to each of the fuel cells 10 individually to flow into thehousing 20.

Further, the embodiment adopts structure where the lower supply manifold100, the lower discharge manifold 104, the upper supply manifold 102,and the upper discharge manifold 106 are provided as the supplymanifolds for guiding the fuel gas such as the hydrogen into the housing20, and discharge manifolds for discharging the fuel gas from thehousing 20, and the supply manifolds and the discharge manifolds areprovided for both of the lower housing member 12 and the upper housingmember 16. In this manner, fuel gas is supplied into, and dischargedfrom the lower MEA 22 a and the upper MEA 22 b individually.Alternatively, for example, a single supply manifold may be provided forthe upper housing member 16, and a single discharge manifold may beprovided for the lower housing member 12.

In this case, it is adequate to provide the two connection holes in thearea where there is no unit cell 50 of the lower MEA 22 a and the upperMEA 22 b to distribute/supply the fuel gas such as the hydrogen from theupper housing member 16 to the lower MEA 22 a through one connectionhole, and allow the excessive fuel gas from the upper MEA 22 b to flowthrough the lower housing member 12 through the remaining one connectionpassage for merging the excessive fuel gas from the upper MEA 22 b andthe excessive fuel gas from the lower MEA 22 a together and dischargingthe fuel gas. By adopting this structure, it becomes possible to reducethe number of component parts, and assemble the fuel cell easily.

DESCRIPTION OF REFERENCE NUMERALS

-   10: fuel cell-   12: lower housing member-   14: support panel-   16: upper housing member-   18: fan attachment member-   20: housing-   22 a: lower MEA-   22 b: upper MEA-   24: electrolyte membrane-   26: anode-   28: cathode-   36: An side groove-   44: interconnecting section-   48: Ca side groove-   50: unit cell-   52: An side film-   54: Ca side film-   56: laminate layer-   60: first straight segment-   62: second straight segment-   64: An side breathing hole-   66: Ca side breathing hole-   70: air supply layer-   72: lower protrusion-   74: upper protrusion-   76: fin-   78 a: upper air supply channel-   78 b: lower air supply channel-   80: discharge duct-   82: inlet duct-   84: lower side hydrogen supply layer-   86: upper side hydrogen supply layer-   88: lower side hydrogen supply channel-   90: onward channel-   92: return channel-   94: connection channel-   96: upper side hydrogen supply channel-   100: lower supply manifold-   102: upper supply manifold-   104: lower discharge manifold-   106: upper discharge manifold-   108: fan

What is claim is:
 1. A fuel cell comprising a membrane electrodeassembly, the membrane electrode assembly comprising: a singleelectrolyte membrane in which interconnecting sections are formed, theinterconnecting sections extending in a first direction and havingconductivity in a membrane thickness direction of the electrolytemembrane; a plurality of anodes extending in the first direction, anddisposed remotely from each other in a second direction perpendicular tothe first direction; a plurality of cathodes extending in the firstdirection, and disposed remotely from each other in the seconddirection, wherein each of the anodes and the cathodes comprises acatalyst layer and a gas diffusion layer, each of the cathodes comprisesa cathode side protection layer facing the electrolyte membrane, whereinthe cathode side protection layer comprises a plurality of auxiliaryholes arranged along the first direction, and wherein the plurality ofauxiliary holes in the cathode side protection layer are in alignmentwith the interconnecting sections, and portions of each of the anodesare in alignment with the interconnecting sections and are free from thecatalyst layer, and the membrane electrode assembly has a zigzag layoutwhere, in the second direction, part of one of the anodes faces part ofone of two cathodes that are adjacent to each other, among the cathodes,through the electrolyte membrane and another part of the one anode facespart of the remaining one of the two cathodes through one of theinterconnecting sections formed in the electrolyte membrane; a cathodeside porous film made of resin and configured to cover the gas diffusionlayer of each cathode of the plurality of cathodes, the cathode sideporous film having breathing holes for supplying an oxygen-containinggas to the plurality of cathodes; and an oxygen-containing gas supplylayer provided adjacent to the cathode side porous film, and anoxygen-containing gas supply channel as a passage of theoxygen-containing gas being formed in the oxygen-containing gas supplylayer, wherein the cathode side porous film is provided between the gasdiffusion layer and the oxygen-containing gas supply layer, and whereinthe cathode side porous film holds, on a surface facing the gasdiffusion layer, at least part of water produced at the cathode, anddischarges the at least part of water to the oxygen-containing gassupply channel through the breathing holes.
 2. The fuel cell accordingto claim 1, wherein the oxygen-containing gas supply channel extends inthe first direction.
 3. The fuel cell according to claim 1, furthercomprising: a negative pressure generation unit configured to cause theoxygen-containing gas supply channel to have a negative pressure.
 4. Thefuel cell according to claim 1, wherein the cathode side porous film ismade only of insulating resin.
 5. The fuel cell according to claim 4,comprising: a second membrane electrode assembly, wherein the membraneelectrode assembly is a first membrane electrode assembly; and a secondcathode side porous film provided to the second membrane electrodeassembly, wherein the cathode side porous film is a first cathode sideporous film provided to the first membrane electrode assembly; whereinthe first cathode side porous film and the second cathode side porousfilm face each other across the oxygen-containing gas supply layer,wherein the oxygen-containing gas supply layer comprises: a firstprotrusion that protrudes toward the first cathode side porous film andcontacts the first cathode side porous film, and a second protrusionthat protrudes toward the second cathode side porous film and contactsthe second cathode side porous film, wherein the first protrusion andthe second protrusion form a wavy fin, wherein the first cathode sideporous film is formed with the breathing holes at positionscorresponding to where the second protrusion and the second cathode sideporous film contact each other, and wherein the second cathode sideporous film is formed with the breathing holes at positionscorresponding to where the first protrusion and the first cathode sideporous film contact each other.
 6. The fuel cell according to claim 1,comprising: a second membrane electrode assembly, wherein the membraneelectrode assembly is a first membrane electrode assembly; and a secondcathode side porous film provided to the second membrane electrodeassembly, wherein the cathode side porous film is a first cathode sideporous film provided to the first membrane electrode assembly; whereinthe first cathode side porous film and the second cathode side porousfilm face each other across the oxygen-containing gas supply layer,wherein the oxygen-containing gas supply layer comprises: a firstprotrusion that protrudes toward the first cathode side porous film andcontacts the first cathode side porous film, and a second protrusionthat protrudes toward the second cathode side porous film and contactsthe second cathode side porous film, wherein the first protrusion andthe second protrusion form a wavy fin, wherein the first cathode sideporous film is formed with the breathing holes at positionscorresponding to where the second protrusion and the second cathode sideporous film contact each other, and wherein the second cathode sideporous film is formed with the breathing holes at positionscorresponding to where the first protrusion and the first cathode sideporous film contact each other.
 7. The fuel cell according to claim 1,wherein an interconnecting section is arranged at each auxiliary hole ofthe plurality of auxiliary holes of the cathode side protection layer.